1. Field of the Invention
The present invention relates to a movie on demand system and video conferencing system of the type wherein multiple clients are serviced by video streams delivered from a central video server.
2. Related Art
In many movie on demand systems and video conferencing systems, multiple clients are serviced by video streams delivered from a central video server. This process (serving multiple clients from a single stream) is referred to as multicasting. In such systems, video is typically delivered by the server to clients in either of two ways: "client pull" or "server push". In a client pull mechanism, the server delivers blocks at the request of the clients. In contrast, in a server push mechanism, the server delivers blocks periodically to the clients. A discussion of client pull and server push strategies can be found in the paper "A Preliminary Study of Push vs. Pull in Motion Video Servers", Second Workshop on High Performance Communication Subsystems, HPCS`93,Williamsburg, Va., September 1993, by K. Hwang et al.
The client pull mechanism incurs additional messages since a client has to notify the server its readiness to receive a new block.
The server push mechanism on the other hand may send a new data block to clients even when earlier blocks are not processed (played back). This is because the play back rate is not the same for all compressed data blocks. Therefore, a larger amount of buffer is required in each client to avoid buffer overflow problem.
The issues are similar in an applications such as teleconferencing, where the same data stream is multicast to multiple clients.